1. Field of the Invention
This invention relates to supported or bound heteropoly acid catalyst compositions, a method of making such catalyst compositions and a process for the oxidation of unsaturated aldehydes, such as methacrolein, to unsaturated carboxylic acids, such as methacrylic acid, in a vapor phase reaction using such catalyst compositions.
2. Description of the Prior Art
Various catalysts are known for the gas phase catalytic oxidation of unsaturated aldehydes to unsaturated carboxylic acids. Included are molybdenum-based mixed metal oxides compound which can contain oxides of metals such as phosphorus, arsenic, cesium, rubidium, cobalt, nickel, iron, chromium, antimony, tellurium and silicon in addition to molybdenum. These same metals and others may occur in heteropoly acid compounds as metal oxide clusters forming heteropolyoxoanions in acid form instead of simple metal oxides. Heteropoly acid compounds are also known as catalysts for the gas phase catalytic oxidation of unsaturated aldehydes to unsaturated carboxylic acids. Heteropoly acid compounds have a central metal atom surrounded by a framework of other metal atoms connected to each other and the central metal atom through oxygen atoms. The central metal atom is different (“hetero”) from the framework metal atoms.
U.S. Pat. No. 3,998,876 discloses a catalyst of a heteropoly acid compound containing phosphorus, molybdenum, arsenic, at least one of vanadium, tungsten, copper, iron, manganese or tin, at least one of lithium, sodium, potassium, rubidium or cesium and ammonium groups in the form of a salt of the heteropoly acid. The examples of the nonsupported catalyst were shown to have a higher degree of conversion at comparable selectivities compared to a catalyst supported on an alumina/silica carrier.
U.S. Pat. No. 4,320,227 discloses a heteropoly acid catalyst containing molybdenum, vanadium, phosphorus, one or more of copper, tin, thorium, aluminum, germanium, nickel, iron, cobalt, zinc, titanium, lead, rhenium, zirconium, cerium, chromium, bismuth or arsenic, and one or more of potassium, rubidium, cesium or thallium. For improvements in thermal stability and catalyst life and increase in yield of methacrolein and methacrylic acid a suitable carrier, such as silicon carbide, α-alumina, aluminum powder, diatomaceous earth or titanium oxide, can be used. Active carriers which react with heteropoly acids are not preferable.
U.S. Pat. No. 5,191,116 discloses a heteropoly acid catalyst containing molybdenum, vanadium and/or copper, phosphorus and/or arsenic, at least one of an alkali metal, such as lithium, sodium, potassium, rubidium, and cesium, an alkaline earth metal, such as magnesium, calcium, strontium and barium, or thallium and at least one of silver, zinc, cadmium, titanium, zirconium, niobium, tantalum, chromium, tungsten, manganese, iron, cobalt, nickel, boron, aluminum, germanium, rhodium, tin, antimony, bismuth, selenium, tellurium, yttrium, lanthanum, cerium, praseodymium and neodymium. The catalysts may be carried on a carrier, such as silica, α-alumina, titania, zirconia, diatom earth, silica alumina, water soluble silica sol and silicon carbide. Inert carriers having a vast plurality of macropores and high porosity are preferred. One working example used a carrier of silica.
U.S. Pat. Nos. 3,939,096 and 3,962,322 disclose a catalyst for a process for vapor phase conversion of an unsaturated aldehyde, such as acrolein, to the corresponding unsaturated carboxylic, such as acrylic acid. The catalyst is unaggolomerarated, supported and of the empirical formula MoaVbWcMndOe where a is 12, b is 0.5 to 12, c is 0.1 to 6, d is 0.5 to 20 and e is 37 to 94. The support is porous silica particles having a surface area of from about 25 to about 350 m2/gm and a porosity of from about 0.2 to about 1.0 cc/gm. Conversion of methacrolein to methacrylic acid is disclosed as possible with this catalyst.
U.S. Pat. No. 5,380,932 discloses a process for production of methacrylic acid and methacrolein by gas phase oxidation of isobutane with a catalyst of heteropoly acid catalyst compounds of the formula CuaHbPcModVeOf where a=0.1 to 1, b=0 to 7.8, c=0.8 to 1.2, d=9 to 12, e=0.5 to 3 and f depends on the molar numbers a to e, and/or H8PMo10VO39(II) or its anhydride PMo10VO35. Carrier material for the catalyst may be large porous carrier particles of zirconia, silicon carbide or silica having a pore volume of from 0.05 to 1.0 cm3/g and a surface area of from 0.01 to 1.0 m2/g. The heteropoly acid catalyst contains molybdenum and vanadium with phosphorus as the central atom, without the presence of any other cationic compounds, and especially without the presence of alkali metal and alkaline earth metal compounds.
U.S. Pat. No. 3,761,516 discloses a metal oxide catalyst for the oxidation of unsaturated aldehydes, such as acrolein and methacrolein, to produce the corresponding unsaturated acids, such as acrylic acid and methacrylic acid. The catalyst is a combination of molybdenum, phosphorus and arsenic with aluminum, copper or cobalt as a promoter on a support or carrier having external macro pores. The pores have a diameter of about 10 microns to about 250 microns and preferably represent 20 to 60 percent of the carrier particle exterior surface. The carrier has a surface area of at most 2 m2/g, preferably 0.01 to 1 m2/g, and most desirably 0.02 to 0.5 m2/g.